Green line is the top marginal rate for married couples filing jointly (most years dividends were tax like ordinary income until 2003), orange is the top rate for income from capital gains. The top corporate tax rate is included for comparison. Your marginal tax rate is the rate you pay on the "last dollar" you earn; but when you view the taxes you paid as a percentage of your income, your effective tax rate is less than your marginal rate, especially after you take into account the deductions and exemptions, i.e. income that is not subject to any tax.

Over the years, changing the amount of taxes people pay was accomplished not just by changing rates but by changing the income limits of the tax brackets. Just looking at the top rates does not give the whole picture about who is paying taxes. Before the 1986 tax reform, the income tax had 15 brackets. In the 1930s, there were more than 50. The Wealth Tax Act of 1935, applied the top rate to income over $5 million and had only a single taxpayer: John D. Rockefeller, Jr. As the number of tax brackets decrease, the the top rate was applied to more people over the decades. Since 1987 the income tax brackets were combined so now more than a million people "qualify" for the top marginal rate. If you are interested here is the first 1040 form for 1913.